Spin emission from antiferromagnets and compensated ferrimagnets

Despite their zero net magnetization, antiferromagnets and compensated ferrimagnets have great potential as electrically and optically activated spin sources. The absence of stray fields means that such spin sources can be placed in close proximity to other magnetic elements without disturbing their state. Recent advances have shown that antiferromagnets and compensated ferrimagnets can emit spin current pulses with timescales down to the picosecond range and in the presence of small or zero external magnetic fields. The spin currents emitted by antiferromagnets have been used in actual devices to induce the field-free switching of nearby ferromagnets. Here, we review the different ways of generating a spin current from a magnetically compensated material. We describe the theoretical models for spin generation and the experimental techniques adopted for measuring the spin currents in different time regimes.